Re: [PATCH] netfilter: use per-cpu recursive lock (v10)

Paul Mackerras
2009-04-20T22:42:08Z

Paul E. McKenney writes:

> But a single CPU is acquiring one lock per CPU, so all the increments
> are to one CPU's preempt_count. :-(

OK, I see, so a task can't take more than 255 spinlocks without
overflowing the preempt count, which seems a bit limiting.

There are 6 free bits in the preempt_count currently, so the preempt
count could be expanded to 14 bits, which would be enough for all
current systems. Beyond that I guess we could make preempt_count be a
long and allow bigger counts on 64-bit architectures.

Paul.